Project Summary The enteric nervous system (ENS) is of fundamental importance to human health through its regulation of all aspects of gastrointestinal (GI) function, most notably gut motility. Congenital or acquired abnormalities of the ENS consequently can lead to serious functional GI disorders, including esophageal achalasia, gastroparesis, intestinal pseudo-obstruction, irritable bowel syndrome, Hirschsprung disease, and slow transit constipation. The adult intestine is known to possess neuronal progenitors, but their role and the mechanisms that activate them are unknown. We and others have observed the birth of new neurons in specific experimental injury models, including intestinal inflammation, GI infection, and following focal neuronal ablation. This neurogenic response can serve to replace neurons lost to injury, but it can also produce neuronal hyperplasia which can have significant pathologic consequences. Enteric neurogenesis is thus a double-edged sword that can be leveraged for a beneficial effect but needs to be modulated to limit its consequences. Our preliminary results suggest that experimental colitis in rodents promotes enteric glial cells to undergo a neurogenic transition via a 5-HT4-dependent pathway. However, this process is poorly understood. The overall objective of this proposal is to understand the mechanisms underlying postnatal enteric neurogenesis and its role in GI health and disease. To achieve this goal, we propose the following specific aims: (1) identify the downstream pathways that are activated by 5-HT4 signaling and lead to glial differentiation into neurons; (2) characterize the subpopulations of glial cells present in the intestine and determine the genetic and epigenetic changes that occur during the glia-to-neuron fate switch; and (3) leverage the intestine?s capacity for neurogenesis to treat the hypoganglionic transition zone associated with Hirschsprung disease. A variety of methodologies will be used to achieve these aims, including isolation and culture of enteric glia from reporter mice; in vitro assays using dominant-negative mutants and pharmacologic inhibitors to determine the signaling pathways involved in glial neurogenesis; single cell RNA seq to identify glial cell subpopulations; a dual reporter transgenic system for live cell imaging of glia-to-neuron cell fate transition; analysis of the genetic and epigenetic changes occurring during that transition; and induction of enteric neurogenesis in HSCR bowel to treat transition zone hypoganglionosis. Successful completion of these experiments will significantly enhance our understanding of the mechanisms underlying neurogenesis in the adult intestine, provide insights into the pathophysiology of neurointestinal diseases, identify new targets to modulate neurogenesis in vivo, offer novel approaches for expanding enteric neurons in the hypoganglionic transition zone of HSCR and in other neurointestinal diseases, and improve the in vitro expansion of enteric neuronal progenitors for cell therapy applications.